Method and apparatus for automatically checking electrical condition of workpieces prior to electrocoating process



June 11, 1968 R. A. IGRAS ETAL 3,388,052

METHOD AND APPARATUS FOR AUTOMATICALLY CHECKING ELECTRICAL CONDITION OF WORKPIECES PRIOR To ELECTROCOATING PROCESS Filed July 1 1963 2 Sheets-Sheet 1 Q A .wuwSSu FAYMO/Vfl 4. 16:94.5

A TTORNE'YS 601900 6 smear/ea INVENTORS June 11, 1968 R. A. IGRAS ETAL METHOD AND APPARATUS FOR AUTOMATICALLY CHECKING ELECTRICAL Filed July 1 1963 F/G. Z

2 Sheets-Sheet 2 /47 I45 /43 2s vs: 5

o o 0 o o i MI Aj n 37 z: I39 137 1 I 21" r" H i 'i| PAYMO/VO A. [ERAS GORDON 6. 6730385196 INVENTORS ATTOR/VfYS' United States Patent METHOD AND APPARATUS FOR AUTOMATICAL- LY CHECKING ELECTRIQAL CONBITEON 0F WORKPEECES PRIOR TO ELECTROCOATING PROCESS Raymond A. Igras, Dearborn Township, Wayne County, and Gordon G. Strosberg, Oak Park, Mich, assignors to Ford Motor Company, Dearnorn, Mich, a corporation of Delaware Filed July 1, 1963, Ser. No. 291,743 9 Claims. (Cl. 204-181) This invention relates to electrocoating electrically conductive objects with an organic coating material dispersed in an aqueous bath. In particular, this invention relates to a method for controlling product quality and improving the efliciency in a continuous, or intermittently continuous process of anodic deposition wherein organic film-forming material is thus deposited upon a conductive substrate within an aqueous bath so as to form a substantially water insoluble coating thereon. More particularly, this invention relates to the use of a novel feed control system in combination with an electrocoating process whereby the electrical condition of workpieces entering said bath is automatically checked to determine the capacity of such workpieces for accepting such coating material.

Objects to be coated are individually suspended from and transported by an overhead conveyor which, with suitable connecting devices, is constructed and arranged such that the suspended workpieces successively enter the aqueous bath for coating and are withdrawn for further processing such as sanding, finish coating, etc. While the object is being coated it is positively charged and a direct current fiow of electrical energy is provided between the object and a negative and grounded coating tank or other electrode.

In large scale coating operations such as the application of a prime coat to automobile bodies or other items of mass production the overall length of the conveyor and other considerations make it impractical to isolate the conveyor from ground. Hence, in an anodic system of coating it becomes necessary to provide insulation between the conveyor and the positively charged workpiece. Such insulators from a variety of causes often become ineffective after varying periods of operation. For instance, the accumulation of oil and conductive dust particles can form a conductive connection across an otherwise eifective insulator. Ordinary wear as Well as defective construction and materials may likewise provide defective insulation between workpiece and conveyor. Under these conditions and arrangements the passage through the coating bath of a workpiece that is in significant electrical connection with ground results in a defectively coated object which must be discarded, reprocessed when feasible, or refinished by time-consuming manual techniques.

In accordance with this invention the resistance of the insulation between each workpiece from its conveyor is automatically measured as the workpiece approaches the electrocoating bath. If the resistance of such insulation to the flow of electrical energy is found to be below a pre determined minimum, a warning system is automatically actuated and/ or the conveyor is automatically halted until the defective insulator can be repaired or replaced or the workpiece shifted to another hanger.

Organic coating materials which may be used in the bath include but not by Way of limitation alkyd resins, acrylate resins, phenol-formaldehyde resins and various carboxylic acid resins or mixtures of the foregoing with each other or other film-forming materials including binding agents and extenders conventionally employed with water based paints. Such materials may include or be employed with other organic monomers and/ or polymers including but not by way of limitation hydrocarbons and See oxygen substituted hydrocarbons such as ethylene glycol, propylene glycol, glycerol, carbitol, methanol and various carboxylic acids, ethers, aldehydes and ketones. The filmforming material may include or be employed with pigments, dyes, drying oils, etc. and may be dispersed as a colloid, emulsion or emulsoid.

The organic coating material is dispersed in the bath with the aid of a conventional dispersing agent. These include water soluble ammonium and basic amine salts, polymeric amines, etc. Such materials are described at length in U.S. Patent 2,530,366 to A. G. Gray and elsewhere in the literature.

It is one object of this invention to improve product quality control and promote operational efliciency in an electrocoating process by providing method and means for accurately detecting the approach of inetfectively insulated workpieces and to prevent the same from entering the coating bath.

With the foregoing and other objects in view, as will hereinafter become apparent, this invention comprises the methods, combinations, construction, and arrangement of parts hereinafter set forth, disclosed, claimed and illustrated in the accompanying drawings wherein:

FIGURE 1 is a schematic drawing depicting one embodiment of electrocoating apparatus with which insulation checking apparatus is employed in accordance with the instant invention.

FIGURE 2 is a schematic drawing illustrating an electrical feed control system for use with the electrocoating apparatus of FIGURE 1, said system being adapted to automatically measure the electrical resistance between workpiece and ground, signal the approach of a defective insulator and stop the conveyor when an improperly insulated workpiece approaches the bath.

FIGURE 3 is a schematic drawing illustrating the current measuring device whereby the resistance of an insulator is measured in the feed control system of FIG- URE 2.

Referring now to FIGURE 1, chemically resistant tank 11 contains a coating bath 13 and serves as a negative electrode in the coating process being connected to DC power source 17 via conductor 15. Article 19 which is to be electrocoated is placed upon conductor hanger 21 which in turn is suspended from and transported through bath 13 by a conveyor 23 which may be of the conventional electrically powered, chain driven variety. Hanger 21 includes an insulator 25 which is provided to isolate article 19 from the grounded conveyor. Contact plate or brush 29 is attached to and in electrical connection with hanger 21. Brush 29 rides against and is in electrical contact with insulation check segment '31 of segmented bus bar 33. Although not further divided in the instant drawing it will be understood that bus bar 33 may comprise a plurality of segments electrically insulated from each other some of which may be connected to negative leads from the power source if so desired for manipulation of the coating process.

The portion of the bus bar used to provide current to the workpiece is connected to power source 17 through positive lead or conductor 41.

The potential employed to coat the objects passing through the bath will ordinarily be in the range of about 50 to 1000, preferably to 500, volts.

As article 19 moves from right to left with respect to the drawing and approaches bath 13 brush 29 comes into electrical contact with segment 31 thereby bringing the unit into the monitoring area where the insulation between positively charged article 19 and grounded conveyor 23 is measured.

Referring now to FIGURE 2, article 19 is again shown suspended from conveyor 23 by hanger 21 with brush 29 in electrical connection with bus bar segment 31 between insulators and 37. Conveyor 23 is electrically driven by a conventional power source, not shown, via conductors 131 and 133 and a conventional drive mechanism indicated generally at 135 which comprises electric motor 137, reducer 139, chain 141 and conventional connections therefor, not shown.

A check and control device, indicated generally 147, is adapted to automatically measure the resistance of the conveyor insulator of a bath approaching workpiece and to signal the operator and stop the conveyor if such resistance is below a predetermined value. The resistance measuring mechanism of device 147 is in electrical connection with segment 31 via conductor 143 and with the grounded conveyor 23 through conductor 145. This device is described hereinafter with FIGURE 3.

The resistance measuring mechanism of device 147 is electrically connected to an alternating current power source, not shown, by conductors 149, 153 and 155, and switch 151. Relay coil 157 for activating a set of contacts indicated at 159 is in electrical connection with conductors 153 and 155. The contacts of this set are closed when the conveyor is running and are in electrical connection with conductor 131 of the conveyor circuit. Coil 157 and the set of contacts indicated at 159 provide assurance against the feeding of improperly insulated objects to the bath because of a failure in the power circuit to the resistance measuring device indicated at 147. Upon such failure coil 157 is deactivated causing the set of contacts indicated at 159 to open stopping the conveyor. Signal light 161 is in electrical connection with conductor 153 and with conductor when the set of contacts indicated at 163 is closed. The contacts of this set which are normally open are activated by relay coil 165 which also activates a set of contacts indicated at 167. The contacts of this set are normally closed and are in electrical connection with conductor 13]. of the conveyor circuit. Relay coil 165 is in electrical connection with conductor 155 and in electrical connection with conductor 153 when the set of contacts indicated at 169 is closed. The set of contacts 169 is normally open and is closed via device 147 as illustrated in FIGURE 3.

Referring now to FIGURE 3, conductors 153 and 155 also shown in FIGURE 2 are in electrical connection with a variable transformer 171. The transformer setting is such that the potential provided via conductors 153 and 155, e.g. 110 volts AC, is increased to provide a difference of potential of about 2000 to 3500 volts between conductors and 177 via step-up transformer 173. This voltage is impressed upon insulator 25 via conductor 177, resistors 179, 181, 183 and conductor 185 which are in electrical connection with conductor 143 and via conductor 175, bridge 191 and conductor 193 which are in electrical connection with conductor 145. The electrical connection of conductor 143 with segment 31 and the electrical connection of 145 with conveyor are shown in FIGURE 2. Relay coil 195 of bridge 191 is adapted to cause the aforementioned set of contacts indicated at 169 to close when a predetermined electric current passes through the coil.

In operation an object to be coated represented here by numeral 19 is moved by conveyor 23 into electrical connection with segment 31 via hanger 21 and brush 29. If the electrical resistance of insulator 25 is below a predetermined minimum, sufiicient current will flow through coil 195 via the electrical connections heretofore explained to cause the set of contacts indicated at 169 to close thereby activating relay coil 165. This in turn causes the set of contacts indicated at 163 to close causing warning light 161 to be lit. It is, of course, within the scope of the invention to employ a hell or other audio warning device in addition to or in lieu of light 161. In this embodiment the activation of coil 165 also causes the set of contacts indicated at 167 to open stopping the conveyor.

The foregoing detailed description of this embodiment of apparatus for carrying out the process of this invention is submitted solely for purposes of illustration. Those skilled in the art will be aware that numerous modifications can be made in the aforedescribed system without departing from the spirit and the scope of the invention as expressed in the claims.

What is claimed is:

1. In a method of coating wherein electrically conductive objects transported by and electrically insulated from a conveyor are successively passed through an aqueous bath having organic film-forming material dispersed therein and a first electrode in contact therewith, each of said objects while passing through said bath serving as a second electrode, and providing a unidirectional flow of electrical energy between said first electrode and said second electrode until a substantially water insoluble coating of said material is deposited upon said second electrode, the improvement which comprises causing each of said objects to pass prior to entry into contact with said bath through a resistance measuring zone wherein a difference of electric potential is provided between said object and said conveyor, measuring the resistance to the flow of electrical energy between said object and said conveyor from said difference of potential while said object is in movement through said zone, and utilizing said How between object and conveyor when it exceeds a predetermined value to give warning of the approach of an improperly insulated object to said coating bath.

2. In a method of coating wherein electrically conductive objects transported by and electrically insulated from an endless conveyor are successively passed through an aqueous bath having organic film-forming material dispersed therein and a first electrode in contact therewith, each of said objects while passing through said bath serving as a second electrode, and providing a flow of electrical energy between said first electrode and said second electrode until a substantially water insoluble coating of said material is anodically deposited upon said second electrode, the improvement which comprises causing each of said objects to pass prior to entry into contact with said bath through a resistance measuring zone wherein a diiference of electric potential is provided between said object and said conveyor, measuring the resistance to the flow of electrical energy between said object and said conveyor from said difference of potential while said object is in movement through said Zone, and utilizing said flow between object and conveyor when it exceeds a predetermined value to stop said conveyor.

3. In a method of coating wherein electrically conductive objects transported by and electrically insulated from a conveyor are successively passed through an aqueous bath having an organic film-forming material dispersed therein and a first electrode in contact therewith, each of said objects while passing through said bath serving as a second electrode, providing a difierence of electric potential between said first electrode and said second electrode, and maintaining the resulting flow of electrical energy between said first electrode and said second electrode until a substantially water insoluble coating of said material is deposited upon said second electrode, the improvement which comprises causing each of said objects to pass prior to entry into contact with said bath through a resistance measuring zone wherein a difference of electric potential is provided between said object and said conveyor in excess of the difiference of potential provided between said first electrode and said second electrode in the coating bath, measuring the resistance to the flow of electrical energy between said object and said conveyor as said object passes through said zone, and utilizing said flow between object and conveyor when it exceeds a predetermined value to give warning of the approach of the improperly insulated object to said coating bath.

4. In a method of coating wherein electrically conductive objects transported by and electrically insulated from an endless conveyor are successively passed through an aqueous bath having an organic film-forming material dispersed therein and a first electrode in contact therewith, each of said objects while passing through said bath serving as a second electrode, providing a difference of electric potential between said first electrode and said second electrode, and maintaining the resulting unidirectional flow of electrical energy between said first electrode and said second electrode until a substantially water insoluble coating of said material is deposited upon said second electrode, the improvement which comprises causing each of said objects to pass prior to entry into contact with said bath through a resistance measuring zone wherein a difference of electric potential is provided between said object and said conveyor in excess of the difference of potential provided between said first electrode and said second electrode in the coating bath, measuring the resistance to the flow of electrical energy between said object and said conveyor as said object moves through said zone, and utilizing said flow between object and conveyor when it exceeds a predetermined value to stop said conveyor.

5. In a method of coating wherein electrically conductive objects transported by and electrically insulated from a conveyor are successively passed through an aqueous bath having organic film-forming material dispersed therein and a first electrode in contact therewith, each of said objects while passing through said bath serving as a second electrode, providing a difference of electric potential between said first electrode and said second electrode, and maintaining the resulting flow of electrical energy between said first electrode and said second electrode until a substantially water insoluble coating of said material is anodically deposited upon said second electrode, the improvement which comprises causing each of said objects to pass prior to entry into said bath through a resistance measuring zone wherein electrical contact is established with an electrical circuit adapted to automatically measure resistance to flow of electrical energy between the object and said conveyor and to automatically signal the approach of an object to said bath having an electrical connection with said conveyor sufiicient to admit therebetween at said potential a flow of electrical energy in excess of a predetermined value.

5. Apparatus for use in coating electrically conductive objects comprising in combination a coating tank adapted to retain an aqueous bath having organic film-forming material dispersed therein, a first electrode positioned to be in contact with said bath when said tank is charged with said bath, conveyor means for transporting a line of electrically conductive objects electrically insulated therefrom into said tank, means for providing a fiow of electrical energy, between each of said objects and said first electrode when the given object and said first electrode are in contact with said bath, means for providing a difierence of electric potential between each of said objects and said conveyor prior to the entry of each such object into said tank, means for measuring the flow of electrical energy between each such object and said conveyor while the object is in movement to said tank and means for utilizing said flow between object and conveyor when it exceeds a predetermined value to give warning of the approach of an improperly insulated object to said coating bath.

'7. Apparatus for use in coating electrically conductive objects comprising in combination a coating tank adapted to retain an aqueous bath having organic film-forming material dispersed therein, a first electrode positioned to be in contact with said bath when said tank is charged with said bath, conveyor means for transporting a line of electrically conductive objects electrically insulated therefrom into said tank, means for providing a flow of electrical energy between each of said objects and said first electrode when the given object and said first electrode are in contact with said bath, means for providing a difference of electric potential between each of said objects and said conveyor prior to the entry of each such object into said tank, means for measuring the flow of electrical energy between each such object and said conveyor while the object is in movement to said tank and means for utilizing said flow between object and conveyor when it exceeds a predetermined value to stop the conveyor.

3. Apparatus for use in coating electrically conductive objects comprising in combination an electrically conductive coating tank adapted to retain an aqueous bath having organic film-forming material dispersed therein and to serve as a first electrode, conveyor means for transporting a line of electrically conductive objects insulated therefrom into said tank, means for providing a flow of electrical energy between each 'of said objects and said tank when the object is in contact with said bath, means for providing a difference of electric potential between each of said objects and said conveyor prior to the entry of each such object into said tank, means forme-asuring the flow of electrical energy between each such object and said conveyor while said object is in movement to said tank and means for utiliz ing said flow when it exceeds a predetermined value to give warning of the approach of an improperly insulated object to said coating tank.

9. Apparatus for use in coating electrically conductive objects comprising in combination an electrically conductive coating tank adapted to retain an aqueous bath having organic film-forming material dispersed therein and to serve as a first electrode, conveyor means for transporting a line of electrically conductive objects insulated therefrom into said tank, means for providing a flow of electrical energy between each of said objects and said tank when the object is in contact with said bath, means for providing a difference of electric potential between each of said objects and said conveyor prior to the entry of each such object into said tank, means for measuring the flow of electrical energy between each such object and said conveyor while said object is in movement to said tank and means for utilizing said flow when it exceeds a predetermined value to stop said conveyor.

References Cited UNITED STATES PATENTS 8/1965 Burnside et al. 204181 8/1965 Oster 204-181 

1. IN A METHOD OF COATING WHEREIN ELECTRICALLY CONDUCTIVE OBJECTS TRANSPORTED BY AN ELECTRICALLY INSULATED FROM A CONVEYOR ARE SUCCESSIVELY PASSED THROUGH AN AQUEOUS BATH HAVING ORGANIC FILM-FORMING MATERIAL DISPERSED THEREIN AND A FIRST ELECTRODE IN CONTACT THEREWITH, EACH OF SAID OBJECTS WHILE PASSING THROUGH SAID BATH SERVING AS A SECOND ELECTRODE, AND PROVIDING A UNIDIRECTIONAL FLOW OF ELECTRICAL ENERGY BETWEEN SAID FIRST ELECTRODE AND SAID SECOND ELECTRODE UNTIL A SUBSTANTIALLY WATER INSOLUBLE COATING OF SAID MATERIAL IS DEPOSITED UPON SAID SECOND ELECTRODE, THE IMPROVEMENT WHICH COMPRISES CAUSING EACH OF SAID OBJECTS TO PASS PRIOR TO ENTRY INTO CONTACT WITH SAID BATH THROUGH A RESISTANCE MEASURING ZONE WHEREIN A DIFFERENCE OF ELECTRIC POTENTIAL IS PROVIDED BETWEEN SAID OBJECT AND SAID CONVEYOR, MEASURING THE RESISTANCE TO THE FLOW OF ELECTRICAL ENERGY BETWEEN SAID OBJECT AND SAID CONVEYOR FROM SAID DIFFERENCE OF POTENTIAL WHILE SAID OBJECT IS IN MOVEMENT THROUGH SAID ZONE, AND UTILIZING SAID FLOW BETWEEN OBJECT AND CONVEYOR WHEN IT EXCEEDS A PREDETERMINED VALUE TO GIVE WARNING OF THE APPROACH OF AN IMPROPERLY INSULATED OBJECT TO SAID COATING BATH. 